Heretofore, in a process for obtaining an adduct of imidazole-isocyanuric acid, water, aqueous solution of acetic acid, or dimethylformamide is used as a solvent. An imidazole compound and isocyanuric acid are charged into the solvent as it is in a solid to react by addition, and then crystallized while cooling, thereby being obtained an adduct of imidazole-isocyanuric acid. (confer JP-A-53-116391).
However, the conventional process has been problematic, since the adduct of imidazole-isocyanuric acid produced is remarkably poor in solubility in the solvents, whereby the adduct of imidazole-isocyanuric acid crystallizes before starting materials are dissolved, and the starting materials are taken into the adduct, resulting in that there is required a troublesome operation such as recrystallization, etc. in order to obtain a product having high purity. Further, to obtain a product having high purity by one operational step, it has been prepared by a process in which a reaction is carried out in a homogeneous system by employing a large amount of solvents, and then product is crystallized. However, the process cannot provide a large amount of the product, resulting in that efficiency of a reactor is very low. Still further, since reaction yield is also low, there is a problem in view of being economically disadvantageous.
In addition, there is described a process in which a polyepoxy resin is directly mixed with an imidazole compound and isocyanuric acid with a roll (confer JP-A-61-235426). However, the process includes a problem that isocyanuric acid does not readily react by addition to an imidazole compound because isocyanuric acid does not sufficiently dissolve into the epoxy resin, resulting in that the adduct of imidazole-isocyanuric acid cannot exhibit inherent functions as a curing agent.